Duke Henry's son Henry II "the Quarreller" from 974 onwards, revolted against his cousin Emperor Otto II, whereupon he was deposed as Duke of Bavaria in favour of Otto's nephew Duke Otto I of Swabia. At the same time Emperor Otto II created a sixth duchy in addition to the original stem duchies, the new Duchy of Carinthia. He reverted the possession of the territories to the Luitpoldings, when he split Carinthia from the Bavarian lands and installed the former Duke Berthold's son Henry III the Younger as duke in 976. The duchy then comprised a vast territory including the marches of Styria (marchia Carantana), Carniola and Istria as well as the March of Verona in the former Kingdom of Italy. Nevertheless Henry III was the first and also the last Luitpolding duke; he chose to join the unsuccessful War of the Three Henries against Emperor Otto II, he lost Carinthia two years later and was succeeded by the Emperor's nephew Otto I, a scion of the Salian dynasty. Though Henry III once again managed to regain the ducal title in 985, Carinthia upon his death in 989 fell back to the Imperial Ottonian dynasty of Bavaria.

Duchy of Carinthia at its maximum expansion

Carinthia however remained a separate entity, and in 1012 Count Adalbero I of Eppenstein, Margrave of Styria since about 1000, was vested with the duchy by Emperor Henry II, while the Istrian march was separated and given to Count Poppo of Weimar. Adalbero was removed from office in 1035 after he had fallen out of favour with the Salian Emperor Conrad II. In 1039 Carinthia was inherited by Emperor Henry III himself, who split off the Carniolan march the following year and granted it to Margrave Poppo of Istria. In 1077, the duchy was given to Luitpold, again a member of the Eppensteiner family, which, however, became extinct with the death of Luitpold's son Henry III of Carinthia in 1122. Upon his death the duchy was further reduced in area: a large part of the Eppenstein lands in what is today Upper Styria passed to Margrave Ottokar II of Styria.

The remainder of Carinthia passed from Duke Henry III to his godchild Henry from the House of Sponheim, who ruled as Henry IV, from 1122 to his early death the following year.[1] The most outstanding of the Spanheim dukes was Bernhard, the first Carinthian duke who was actually described and honoured in documents as "prince of the land".[1] The last Spanheim duke was Ulrich III; he signed an inheritance treaty with his brother Archbishop Philip of Salzburg, who however could not prevail against the Bohemian king Ottokar II Přemysl. In spite of being supported by the German king Rudolph of Habsburg, who defeated Ottokar II at the Battle on the Marchfeld in 1278, Philip never gained actual power. The duchy was seized by Rudolph and Philip died a year later in 1279.

Rudolph, after being elected King of the Romans and defeating King Ottokar II, at first gave Carinthia to Count Meinhard II of Gorizia-Tyrol. In 1335, after the death of Henry, the last male of this line, Emperor Louis the Bavarian gave Carinthia and the southern part of the Tyrol as an imperial fief to the Habsburg family on May 2 in Linz. The Habsburgs would continue to rule Carinthia until 1918. As with the other component parts of the Habsburg Monarchy, Carinthia remained a semi-autonomous state with its own constitutional structure for a long time. The Habsburgs divided up their territories within the family twice, according to the 1379 Treaty of Neuberg and again in 1564. Each time, the Duchy of Carinthia became part of Inner Austria and was ruled jointly with the adjacent duchies of Styria and Carniola.

Early 18th century map of Carinthia showing fiefs owned by Salzburg and Bamberg.

Over the centuries, the German language, which carried more prestige, expanded at the expense of Slovene, but the fact that in the 16th century the Estates of Carinthia could still point out that Carinthia was "a WindicArchduchy", i.e. a sovereign Slovene principality, shows that the Carinthian people were aware of their ancient and pre-German roots.

Following the end of the war and the dissolution of Austria-Hungary, the 1919 Treaty of Saint-Germain stipulated the Carinthian Canal Valley stretching from Tarvisio as far as Pontafel (172 square miles)[3] go to Italy and that the Slovene-speaking areas of the Meža Valley, the Drava Valley area around Unterdrauburg, which was afterwards renamed Dravograd, and the Jezersko area (128 square miles of territory) [3] be ceded to the new SHS-State. The Kingdom of Serbs, Croats and Slovenes, however, was not satisfied with these parts of the former duchy and also occupied land north of the Karawanken mountain range, including the capital city of Klagenfurt. The Entente powers decided on a two-stage referendum, of which the first stage, the Carinthian Plebiscite was held on October 10, 1920 to determine the fate of Carinthia. The outcome in favour of Austria did not change the borders as decided upon in the Treaty of Saint-Germain.